Many conventional trench shields had been disclosed for protecting side walls of a trench excavation against collapse. However, they are complex in structure and not mobile in the trench, thereby being inconvenient for use in a construction site especially in a pipe construction work.
U.S. Pat. No. 5,306,103 (hereinafter called as "prior art") to Spencer disclosed a wheeled carriage assembly for trench shield having protective panels (18) hung on an axle members (30) of a plurality of wheels (52) which are rolling on a ground surface (22) adjacent the trench. Such a wheeled carriage assembly may suspend and support a trench shield for advancement along an excavated trench such as for laying a pipe (16) in the trench.
However, the ground surface near the trench excavation may always be placed or piled with excavated materials, soil and stones to become an uneven ground surface, easily obstructing the forward movement of the conventional wheeled carriage assembly (prior art) and thereby decreasing the efficiency of an engineering construction work.
The present inventors have found the drawbacks of the prior art and invented the present trench shield directly ridable and movable on a constructing pipe.